Conventional Aqueous Development Systems
In conventional "wet" or aqueous silver halide based color photographic processing systems, an imagewise exposed photographic element, for example color paper designed to provide color prints, is processed in a color developer solution. The developer reduces the exposed silver halide of the photographic element to metallic silver and the resulting oxidized developer reacts with incorporated dye-forming couplers to yield dye images corresponding to the imagewise exposure. As silver is generally gray and desaturates the pure colors of the dyes, it is desirable to remove it from the dye images. Silver is conventionally separated from the dye images by a process of bleaching the silver to a silver salt and removing the silver halide by using an aqueous solvent, a fixing bath. This fixing bath also removes the undeveloped original silver halide. Commonly, the bleach and fix are combined into one solution, a bleach-fix solution. Bleach-fix solutions commonly contain iron, ammonium, EDTA (ethylenediaminetetraacetic acid), thiosulfate and, after use, silver ion. These components of "wet" or aqueous silver halide processing can be the source of much of the pollution from photofinishing processes.